The objectives of the proposal are to evaluate the "normal" barrier function of the airway mucosa and elucidate pathways for uptake and transport of large polar solutes across the epithelial barrier. We intend to accomplish these objectives by a combined morphologic and physiologic study of the bidirectional movement of horseradish peroxidase (HRP, 40,000 daltons), 3H-dextran (10,000 daltons) and 14C-mannitol (182 daltons) across the tracheal epithelium in-vitro studies employing Ussing like tubular chambers. The movement of HRP will be monitored by radioimmunoassay whil 14C-mannitol and 3H-dextran measured by liquid scintillation Beta spectrometry. Trascellular and paracellular uptake of HRP will be assessed by trnsmission electron microscopy while tight junctional configuration evaluated by freeze etching techniques. Using physical and chemical stimuli that may selectively perturbate transcellular or paracellular flow of probes, we will partition overall transport of large polar solutes into the paracellular and transcellular compartments. In studies utilizing pilocarpine, the quantitative relationship between goblet cell number and their secretory activity and lrge solute permeability will be investigated. Finally, we will study the effects of immediate allergic reaction and its putative mediators on large solute permeabvility and mucous glycoprotein secretion in-vitro. These proposed studies may enhance our knowledge of the protective barrier function of the airway mucosa and cellular and subcellular factors that regulate movement of exogenous and endogenous macromolecules across the airway epithelia.